This application relates to spin torque transfer devices.
Spin electronics has attracted much research and industrial interest in the last decade. In spin electronics, the spin of an electron, rather than the charge, is used to indicate the presence of digital information. The digital information or data, represented as a “0” or “1”, is storable in the alignment of magnetic moments within a magnetic element and is represented as the resistive state of the magnetic element, which depends on the magnetic moment's alignment or orientation. The stored information or data is read from the element by detecting the magnetic element's resistive state. A more recent development of spin electronics is the spin transfer torque technology, which is a method to manipulate the electron spin and magnetic orientation of electronic devices and therefore the stored information.
The magnetic element, in general, includes a ferromagnetic pinned layer and a ferromagnetic free layer, each having a magnetization orientation, and a non-magnetic barrier layer therebetween. The magnetization orientations of the free layer and the pinned layer define the resistance of the overall magnetic element. Such an element is generally referred to as a “spin tunneling junction,” “magnetic tunnel junction” or the like. When the magnetization orientations of the free layer and pinned layer are parallel, the resistance of the element is low. When the magnetization orientations of the free layer and the pinned layer are antiparallel, the resistance of the element is high.
The magnetization orientation of the free layer is conventionally controlled by an external magnetic field. Recently-observed spin transfer torque effect shows that a DC current or current pulse through the magnetic element can also be used to manipulate the free layer magnetization orientation. Under a sufficiently large current, the free layer magnetization orientation stabilizes along the parallel direction with respect to the pinned layer magnetization orientation when electrons flow from the pinned layer to the free layer, vice versa. To read out the resistance of the magnetic element, a current-perpendicular-to-plane (CPP) configuration is used, in which a small current is driven perpendicular to the layers of the magnetic element. Because of the small size of the magnetic elements and the close spacing of adjacent elements, care must be taken that current applied to one magnetic element does not inadvertently affect an adjacent magnetic element.
At least because of their small size, it is desirous to use magnetic logic elements in many applications. It has been proposed that these spin electronic devices using magnetic fields could be used as logic devices. However, there are deficiencies in the proposed designs. Complex logic functions (such as an XOR function) can not be realized using the design of magnetic logic devices employing magnetic fields. The present disclosure provides improved programmable or reconfigurable magnetic logic device that utilize input current passed through magnetic elements.